A semiconductor memory device has a function of driving output data with a driving force appropriate for external matters, by using an output driver when it is necessary to output data.
The driving force is a force for driving the voltage level of output data toward the levels of external voltages, VDD and VSS. As the driving force increases, the voltage level of output data approaches the levels of the specified external voltages, VDD and VSS. The driving force may be divided into a pull-up driving force as a force for driving the voltage level of an output signal toward the level of a power supply voltage VDD, and a pull-down driving force as a force for driving the voltage level of the output signal toward a ground voltage (VSS. In order to control the voltage of the output data outputted from an output driver to a desired level, it is necessary to control the driving force.
Since the driving force of the output driver may change due to variations in process, voltage and temperature (PVT) properties, the output driver is required to have a function that controls the driving force in conformity with variations in PVT properties.
FIG. 1 is a block diagram showing the configuration of a conventional output driver.
Referring to FIG. 1, the conventional output driver includes a driving unit 1 configured to pull-up drive or pull-down drive output data DOUT according to the level of input data DIN, and a fuse signal generation unit 2 configured to detect the level of the output data DOUT and generate fuse signals FUSE<1:N> in order to control the driving force of the driving unit 1.
In the conventional output driver configured in this way, the driving force is controlled according to the fuse signals FUSE<1:N> which are generated by the fuse signal generation unit 2, to cope with a change of the driving force due to variations in PVT properties. During a preliminary test, the level of the output data DOUT is detected and the fuses included in the fuse signal generation unit 2 are programmed, by which the driving force of the output driver is controlled.
However, in the conventional output driver, preliminary testing for controlling the driving force should be performed, and a fuse circuit should be provided, causing area utilization efficiency to deteriorate. Reprogramming after completion of programming of the fuse circuit is not an option.